"When we questioned the patient to find out the source of this infection, we discovered that he was a keen gardener and had lacerated his left index finger two days before the onset of his symptoms, while planting with compost," they wrote. "We presumed that this cut was the site of entry of the organism."

The patient's condition improved, and seven days later he was moved to a respiratory ward before being discharged.

Legionnaires' disease is normally caused by the bug Legionella pneumophili, which lives naturally in rivers, lakes, and reservoirs, and can also be found in man-made structures containing water such as air conditioning systems. Legionella longbeachae is a less common species first isolated from a patient in Long Beach, California. Unlike its cousin, it is mostly found in soil and potting compost. Infection by this type of Legionnaires' bug is sometimes called Pontiac Fever.

In the UK, just nine cases have been reported since 1984. L. longbeachae infections are much more common in Australia, New Zealand and Japan, where it accounts for about 30% of all cases of Legionnaires' disease. They added: "The UK Royal Horticultural Society has issued warnings about the risk of contracting Legionnaires' disease from handling compost and has announced that bags of potting compost will carry cautionary statements."